1) Field of the Invention
This invention relates in general to a metal diaphragm valve for gas supply pipings, and more particularly to such a valve for use in semiconductor chip manufacturing facilities.
2) Description of the Prior Art
There has been increasing demand for micronized metal diaphragm valves for the gas pipings of semiconductor chip manufacturing equipments. Since such a valve is normally operated under extremely highly pressurized condition, the valve is required to develop force enough to overcome the pressure of the hydraulic system exerted on the diaphragm particularly when the valve is actuated to bring the diaphragm toward the valve seat. In conventional technologies, large pneumatic cylinders have been employed to generate high pressure to actuate the diaphragms. Another attempt made to develop large pneumatic pressure for metal diaphragm valves is the type which uses dual pneumatic cylinders as shown in FIG. 5. In either case, the device has been found to have a large overall dimension.
Fresh improvements have since been proposed to provide a small valve drive system capable of developing boosted force in closing operation. One such an example is illustrated in FIG. 6. In the drawing, a metal diaphragm valve (m) includes a pneumatic cylinder (a) having a reciprocating piston (b). A movable shaft (c) is axially affixed to the piston (b) for movement back and forth therewith when the cylinder (a) is pneumatically operated. The shaft (c) is pivotally connected to a lever (e) that is coupled to a cam plate (g) through a pivot (f) that lies slightly off from the center of the cam plate (g). The cam plate (g) is rotatably supported by ball bearings (h) that are arranged to surround the cam plate. A push rod (i) is vertically movably disposed, which is mounted in constant contact at an upper end thereof with the cam (f).
The horizontal movement of the piston (b) is converted through the lever (e) to the cam plate (g) which in turn rotates about the pivot (f) causing the push rod (i) up and down. The vertically reciprocating push rod (i) has a lower end which is used to operate a metal diaphragm (not shown) of the valve (m). The cam plate arrangement is designed to generate greater force to cause the diaphragm to close than the force originally produced by the pneumatic cylinder by first converting it into a rotational movement.
However, the above attempt also has proved to pose problems. For example, the mechanisms developed are complex in design and need many components.